It is known that high critical temperature superconductive materials with compositions that generally satisfy the formulae: EQU Ln.sub.2 Ba.sub.4 Cu.sub.(6+n) O.sub.(14-n)
or EQU (BP).sub.2 Sr.sub.2 Ca.sub.n Cu.sub.(1+n) O.sub.(6+2n)
where
Ln=lanthanide PA1 BP=Bi; Bi.sub.(1-x) Pb.sub.x ; Tl PA1 n=0; 1; 2 PA1 it is lengthy and fiddly; PA1 it may fail utterly if a parameter should vary due to involuntary drift: aging of the material; changes in the raw materials; a change of operator, etc.; PA1 it is necessary to wait until all of the operations have been completed before finding out whether or not the product is satisfactory. PA1 Ln=lanthanide PA1 BP =Bi; Bi.sub.(1-x) Pb.sub.x ; Tl PA1 n=0; 1; 2 PA1 the starting material is a mixture of powders of precursors for said material having stoichiometric proportions appropriate for the desired superconductive phase; PA1 the said mixture is agglomerated to form a tubular or a cylindrical piece; PA1 the agglomerated piece is placed in a controlled-atmosphere oven for synthesizing said superconductive phase; PA1 the conductivity of said piece is measured continuously; PA1 the temperature at which conductivity begins to decrease is exceeded and then the temperature is returned to a value where conductivity begins to increase; and PA1 the temperature of the oven is permanently adjusted so that said conductivity does not decrease. PA1 Ln.sub.2 O.sub.3 where Ln represents a lanthanide PA1 BaCO.sub.3 PA1 SrCO.sub.3 PA1 CaCO.sub.3 or CaO PA1 Bi.sub.2 (CO.sub.3).sub.3 or Bi.sub.2 O.sub.3 PA1 PbCO.sub.3 or PbO or Pb.sub.3 O.sub.4.
have the characteristic of presenting narrow ranges of thermodynamic stability. Thus, during synthesis, if the parameters are not within the proper ranges, mixtures are obtained in which the looked-for superconductive phase is embedded in unwanted superconductive phases having low critical temperature and in other parasitic compounds.
In addition to thermodynamic parameters (oxygen pressure, stoichiometry, and temperature), other parameters act dynamically on synthesis: homogeneity, division state, compacting and purity of the precursor reagents, gas flow distribution, temperature profile as a function of time, involuntary gradients in the treatment oven, and reaction time.
To take account of this state of affairs, operators performing such synthesis proceed as follows: while monitoring the parameters closely, they begin with prior optimization of the material used by varying one of the parameters; then while fixing the parameters as much as possible to the values determined in this way, they perform synthesis in a manner that is reproducible to a greater or lesser extent.
That method suffers from several drawbacks:
An object of the present invention is to seek monitoring means for enabling the operator to track proper operation of synthesis in real time, and in particular for providing a warning at the beginning of any anomaly; it should also be possible to correct synthesis immediately by modifying a parameter such as temperature, oxygen partial pressure, or reaction time.